Resource block candidate selection technique employing packet scheduling in wireless communication systems

ABSTRACT

A method of transmitting data packets over a plurality of dynamically allocated resource blocks in at least one or a combination of a time, code or frequency domain on a shared channel of a wireless communication system, comprising the steps of selecting a number of resource block candidates for potential transmission of data packets destined for a receiver and transmitting the data packet to the receiver using at least one allocated resource block from the selected resource block candidates. The invention also relates to a corresponding method of decoding data packets, a transmitter, receiver and communication system.

This invention relates to shared channel transmission employingpacket-scheduling ARQ (Automatic Repeat reQuest) in mobile/wirelesscommunication systems. It is particularly applicable to downlinktransmission in an OFDMA (Orthogonal Frequency Division Multiple Access)system using ARQ.

In wireless communication systems employing packet-scheduling, at leastpart of the air-interface resources are assigned dynamically todifferent users (mobile stations, MS). Those dynamically allocatedresources are usually mapped onto at least one SDCH (Shared DataCHannel), where a SDCH corresponds to, e.g., the followingconfigurations:

One or multiple codes in a CDMA (Code Division Multiple Access) systemare dynamically shared between multiple MS. Alternatively, one ormultiple subcarriers (subbands) in an OFDMA system are dynamicallyshared between multiple MS.

Combinations of the above two configurations are realized in an OFCDMA(Orthogonal Frequency Code Division Multiplex Access) or a MC-CDMA(Multi Carrier-Code Division Multiple Access) system where codes andsubcarriers (subbands) are dynamically shared between multiple MS.

FIG. 1 shows a packet-scheduling system on a shared channel for systemswith a single SDCH. A PHY Frame reflects the smallest time interval atwhich the scheduler (PHY/MAC Scheduler) performs DRA (Dynamic ResourceAllocation). Further, typically the smallest unit, which can beallocated, is defined by one PHY Frame in the time domain and by onecode/subcarrier/subband in code/frequency domain. In the following, thisunit is denoted as RB (Resource Block). It should be noted that DRA isperformed in the time domain and in the code/frequency domain.

The main benefits of packet-scheduling are firstly multiuser diversitygain by TDS (Time Domain Scheduling). Assuming that the channelconditions of the users change over time due to fast (and slow) fading,at a given time instant the scheduler can assign available resources(codes in case of CDMA, subcarriers/subbands in case of OFDMA) to usershaving good channel conditions. A further benefit is dynamic user rateadaptation. Assuming that the required data rates by the users (servicesa user is running) change dynamically over time, the scheduler candynamically change the amount of allocated resources per user.

For the 3rd Generation CDMA mobile communication systems,packet-scheduling has been introduced by HSDPA (High Speed DownlinkPacket Access) for the 3GPP (UMTS) standard and by HDR (High Data Rate)for the 3GPP2 CDMA 2000 standard.

In addition to exploiting multiuser diversity in the time domain by TDS,in OFDMA multiuser diversity can also be exploited in the frequencydomain by FDS (Frequency Domain Scheduling). This is because the OFDMsignal is in the frequency domain constructed out of multiple narrowbandsubcarriers (typically grouped into subbands), which can be assigneddynamically to different users. By this, the frequency selective channelproperties due to multipath propagation can be exploited to scheduleusers on frequencies (subcarriers/subbands) on which they have a goodchannel quality (multiuser diversity in frequency domain).

For practical reasons in an OFDMA system the bandwidth is divided intomultiple subbands, which consist of multiple subcarriers. Typically, asubband consists of consecutive subcarriers. However, in some cases, itis desired to form a subband out of distributed non-consecutivesubcarriers. The smallest unit on which a user may be allocated wouldhave a bandwidth of one subband and a duration of one PHY frame(consisting of multiple OFDM symbols), which is denoted as a RB(Resource Block). A scheduler may also allocate one or more RBs to auser over multiple consecutive or non-consecutive subbands and/or PHYframes.

E.g., for 3GPP LTE (Long Term Evolution), see, for instance, 3GPP,Technical Report 25.814; Physical Layer Aspects for Evolved UTRA, v.1.0.3, February 2006, which is currently being standardized, a 10 MHzsystem may consist out of 600 subcarriers with a subcarrier spacing of15 kHz, which may then be grouped into 24 subbands (each having 25subcarriers) with each subband occupying a bandwidth of 375 kHz.Assuming that a PHY frame has a duration of 0.5 ms, then a RB would spanover 375 kHz and 0.5 ms.

As seen from the above, in order to exploit multiuser diversity and toachieve scheduling gain in frequency domain, the data for a given usershould be allocated on RBs on which the user has a good channelcondition. Typically, those RBs are close to each other and therefore,this transmission mode is in the following denoted as LM (LocalizedMode). An example LM is shown in FIG. 2.

In contrast to the LM, in OFDMA the resources may also be allocated in adistributed manner in the frequency domain, in the following denoted asDM (Distributed Mode). The DM may be implemented in different ways,e.g., allocating a user (codeblock) on multiple distributed RBs,subcarriers or modulation symbols, and the RBs are shared by multiple DMusers. Further, a user (codeblock) may be allocated on multipledistributed subcarriers or modulation symbols, which are punctured intoa RB used also for LM.

The transmission in DM may be useful in the cases where the channelquality to the mobile stations (receivers) of the RBs is not knownsufficiently well at the base station (transmitter), e.g., due tolimited or poor CQI (Channel Quality Indicator) feedback and/or due tooutdated CQI feedback (e.g., due to high Doppler). A further situationwhere DM may be used is when the data to be transmitted is delaycritical and the transmission should be made robust by utilizingfrequency diversity.

It may be noted that in LM as well as in DM in a given PHY frame,multiple codeblocks (transport-blocks in 3GPP terminology) may beallocated separately to the same user on different RBs, which may or maynot belong to the same service or ARQ process. From a scheduling or DRApoint of view this can be understood as allocating different users.

In the following, it will be focused on OFDMA LM (Localized Mode), wheretypically a codeblock is mapped on a single or multiple consecutive RBs.However, without loss of generality similar is valid for DM, othertransmission modes or access schemes (e.g., CDMA).

In order to efficiently utilize the benefits from scheduling, packetscheduling is usually combined with fast LA (Link Adaptation) techniquessuch as AMC (Adaptive Modulation and Coding) and ARQ (Automatic Repeatrequest). Additionally, fast and/or slow power control may be applied.

Employing AMC (see 3GPP, Technical Report 25.814; Physical Layer Aspectsfor Evolved UTRA, v. 1.0.3, February 2006), the data rate per codeblock(i.e., per PHY Frame) for a scheduled user is adapted dynamically to theinstantaneous channel quality of the respective allocated resource bychanging the MCS (Modulation and Coding Scheme). Naturally, thisrequires a channel quality estimate at the transmitter for the link tothe respective receiver.

In case of OFDMA, the MCS may be adapted per codeblock, which may spanover multiple RBs (in time and/or frequency domain), or may be adaptedper RB.

In order to improve the robustness of the packet data transmission andto recover from transmission errors caused by imperfect AMC operation,generally ARQ is used. ARQ introduces time diversity to thetransmission.

A common technique for error detection/correction is based on ARQschemes together with FEC (Forward Error Correction), called HARQ(Hybrid ARQ). If an error is detected within a packet by the CRC (CyclicRedundancy Check), the receiver requests the transmitter to sendadditional information (retransmission) to improve the probability tocorrectly decode the erroneous packet.

A packet will be encoded with the FEC before transmission. Depending onthe content of the retransmission and the way the bits are combined withthe previously transmitted information three types of ARQ schemes aredefined.

Type I: The erroneous received packets are discarded and a new copy ofthe same packet is retransmitted and decoded separately. There is nocombining of earlier and later received versions of that packet.

Type II: The erroneous received packet(s) is (are) not discarded,instead are stored at the receiver and are combined with additionalretransmissions for subsequent decoding. Retransmitted packets maycontain additional redundancy bits (to lower the effective code rate),may contain (partly) identical bits to earlier transmissions (toincrease reliability of transmitted bits) or may contain a combinationof additional redundancy and repeated bits.

Note that the modulation scheme, code rate and/or the packet size maychange between retransmissions. HARQ Type II is also known asIncremental Redundancy HARQ.

Type III: This type is as special case of Type II with the constraintthat each retransmission is now self-decodable. This implies that thetransmitted packet is decodable without the combination with previoustransmissions. This is useful if some transmissions are damaged in sucha way that almost no information is reusable. If all transmissions carryidentical data this can be seen as a special case, called HARQ Type IIIwith a single redundancy version (or Chase Combining).

The (H)ARQ protocol may be implemented in a synchronous or asynchronousmanner. In the asynchronous ARQ mode, retransmissions may be allocatedon any RB and there is no timing relation with respect to earliertransmission, i.e., retransmissions may be scheduled at any time afterthe transmitter has received a NACK (or an ACK timeout has occurred).Therefore, in case of OFDMA LM, TDS and FDS can be employed forretransmissions achieving scheduling gain by multiuser diversity in thetime and the frequency domain. An example for asynchronous ARQ is shownin FIG. 3. Note that for illustration purposes in this and all followingfigures only one packet transmission to one user is shown.

In the synchronous ARQ mode, retransmissions happen based on apredefined timing relation with respect to the previous transmission andon a predefined RB. The predefined RB may be identical to the RB of theprevious transmission or may be a RB defined according to a pattern.I.e., retransmissions are not scheduled and scheduling gain is notavailable. An example for synchronous ARQ with an ARQ RTT (Round TripTime) of 4 PHY Frames and using the same RB for retransmissions is shownin FIG. 4.

In order to inform the scheduled users about their allocation status,transmission format and data related parameters Layer 1 and Layer 2(L1/L2) control signaling needs to be transmitted along with one ormultiple SDCHs (Shared Data Channels).

In 3GPP HSDPA (CDMA) the L1/L2 control signaling is transmitted onmultiple SCCHs (Shared Control CHannels) in each PHY frame (TTI, 2 ms).Each transmitted SCCH carries information for one scheduled user, suchas channelization-code-set, modulation scheme, transport-block sizeinformation, redundancy and constellation version, HARQ processinformation, new data indicator (similar to a HARQ sequence number) anduser identity.

Generally, the information sent on the L1/L2 control signaling may beseparated into two categories:

The SCI (Shared Control Information) part of the L1/L2 control signalingcontains information related to the resource allocation and it shouldtherefore be possible for all users to decode the SCI. The SCI typicallycontains the information on the user identity and the RB allocation.

Depending on the setup of other channels and the setup of the DCI(Dedicated Control Information), the SCI may additionally containinformation such as ACK/NACK for uplink transmission, MIMO (MultipleInput Multiple Output) related information, uplink schedulinginformation, information on the DCI (resource, MCS, etc.).

The DCI part of the L1/L2 control signaling contains information relatedto the transmission format and to the transmitted data to a specificscheduled user. I.e., the DCI needs only to be decoded by the scheduleduser. The DCI typically contains information on the modulation schemeand the transport-block size (or coding rate).

Depending on the overall channel configuration, the SCI format, and theHARQ setup, it may additionally contain information such as HARQ relatedinformation (e.g., HARQ process information, redundancy andconstellation version, new data indicator), MIMO related information.

The L1/L2 control signaling may be transmitted in various formats:

A first possibility is to jointly encode SCI and DCI. For multiple users(code blocks), the SCIs and DCIs are jointly encoded. For a single user,the SCI and DCI are jointly encoded and transmitted separately for eachuser.

A second possibility is to separately encode SCI and DCI. Hence, theSCIs (or DCIs) for multiple users are encoded jointly or each SCI or DCIis encoded for each user.

In case of having multiple SCI codeblocks (each SCI codeblock maycontain SCIs for multiple users), the SCI codeblocks may be transmittedwith different power, modulation, coding schemes and/or code rates (see3GPP, E-UTRA downlink control channel structure and TP, R1-060378,February 2006).

From a logical point of view, the L1/L2 control signaling contained outof SCI and DCI may be seen, e.g., as follows. A first option would be tohave a single (shared) control channel with two parts (SCI and DCI).Alternatively, a single (shared) control channel (SCI), where the DCI isnot a separate control channel, but part of the SDCH, i.e., mappedtogether with the data (same RB). Further, two separate control channels(SCI, DCI) could exist or multiple separate control channels, e.g.,single SCI control channel and multiple DCI control channels, multipleSCI control channels and multiple DCI control channels or multiple SCIcontrol channels, where the DCI is not a separate control channel, butpart of the SDCH, i.e., mapped together with the data (same RB).

For the purpose of illustration only, the following of this descriptionwill focus on the cases when SCI and DCI are encoded separately, theDCIs are encoded per user (SCIs may be encoded per user or jointly formultiple users) and the DCIs are mapped together with the data (sameRB).

Typically, the SCIs are mapped separately from the SDCH into thephysical resources, whereas the DCI may be mapped separately from theSDCH or into the resources allocated for the SDCH. In the following, thelatter case will be exemplified in FIG. 5, where the DCIs are mapped atthe beginning of the first allocated RB.

Further, as an illustrative example, an OFDMA system with a SDCH (SharedData CHannel), which employs TDS (Time Domain Scheduling) and FDS(Frequency Domain Scheduling), for LM (Localized Mode) transmission willbe assumed.

As shown in FIG. 4, retransmissions in synchronous ARQ operation happenafter a predefined timing of the previous transmission on a predefinedRB. This implies that retransmissions are not scheduled and generallyL1/L2 control signaling (SCI and DCI) is not needed for retransmissions.It should be noted that in some cases it might be beneficial to stilltransmit the DCI with retransmissions in order to adapt the transmissionformat (e.g., modulation scheme, code rate, codeblock size, redundancyversion) for retransmissions. The benefit of no/reduced L1/L2 controlsignaling for retransmissions comes at the cost of lost scheduling gainby TDS and FDS for retransmissions. FIG. 6 shows the case including DCIfor retransmissions.

As illustrated in FIG. 3, retransmissions in asynchronous ARQ operationare explicitly scheduled in time and frequency domain in order toachieve scheduling gain by multiuser diversity not only for initialtransmissions but also for retransmissions. This has the drawback thatfor each retransmission L1/L2 control signaling needs to be transmitted,i.e., SCI and DCI have to be transmitted. If, e.g., 20% of alltransmissions in the system are retransmissions, the L1/L2 controlsignaling overhead compared to synchronous ARQ operation increases bythe same amount. Additionally, in asynchronous ARQ the potential for DRX(Discontinuous Reception) is reduced since the user (receiver) mayreceive retransmissions at any time instant. Therefore, the potentialfor power saving is reduced. FIG. 7 shows an example.

In light of the disadvantages of the conventional communication systems,the object of the present invention is to provide a method oftransmitting and decoding data packets, which increases the schedulinggain in the time, code or frequency domain and reduces the amount ofsignaling data for the transmissions. The object is solved by a methodas set forth in the independent claims.

A further object is to provide a corresponding transmitter and receiveras well as an improved communication system. To this end, the inventionprovides a transmitter, receiver and communication system as defined byindependent claims.

The proposed solution provides the benefits of asynchronous ARQ, wherescheduling gain for retransmissions is available, while reducingrequired control signaling for retransmissions. This is achieved bydefining some resource candidates for retransmissions, where theactually used resource is semi-blindly detected.

Hence, the invention underlies the idea of using resource blockcandidates for transmission and reception and to semi-blind decode theRB candidates in order to detect a data packet destined for thereceiver.

According to a preferred embodiment, the resource block candidatescontain dedicated control information allowing the receiver todistinguish a data packet destined for itself from those destined toother users.

According to a further preferred embodiment, the dedicated controlinformation includes a signature or identity. According to anotherpreferred embodiment, the resource block candidates are eitherpre-configured or depend on a feedback signal received from the user.

Alternatively, the RB candidates can be selected based on a previoustransmission.

In conclusion, the invention can be seen as a “hybrid” or “soft”solution between synchronous and asynchronous ARQ transmission. Withrespect to the conventional and asynchronous ARQ operation, theinvention keeps similar scheduling gain in the time and frequency orcode domain without requiring the transmission of the SCI part of thecontrol signaling for retransmissions. In contrast to synchronous ARQoperation, the invention achieves scheduling gain in the time andfrequency or the code domain.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be further appreciated from the following descriptionof preferred embodiments with reference to the accompanying figures:

FIG. 1 illustrates an example for packet-scheduling with multiplexingfour mobile stations on a SDCH-shared data channel;

FIG. 2 shows an example for TDS and FDS in the localized mode;

FIG. 3 shows an example for asynchronous ARQ;

FIG. 4 shows an example for synchronous ARQ with an RTT of four PHYframes;

FIG. 5 illustrates an example for SCI and DCI control signaling mapping,wherein the DCIs are mapped onto the data part;

FIG. 6 illustrates an example of SCI/DCI signaling for synchronous ARQ;

FIG. 7 shows an example SCI/DCI signaling for asynchronous ARQ;

FIG. 8 illustrates a flowchart illustrating the transmission methodaccording to an embodiment of the invention;

FIG. 9 shows a flowchart illustrating the decoding method according toan embodiment of the invention;

FIG. 10 shows an embodiment of the base station and mobile stationaccording to the invention;

FIG. 11 illustrates an example including SCI/DCI signaling forasynchronous ARQ operation using the principles of the invention;

FIG. 12 illustrates an example for resource block candidate definitionbased on mobile station feedback;

FIG. 13 illustrates an example for localized/vicinity RB candidates; and

FIG. 14 illustrates an example for distributed RB candidates.

DETAILED DESCRIPTION

FIG. 8 shows a flowchart for illustrating the transmitting methodaccording to an embodiment of the invention.

In step 110, resource block candidates for potential transmission of adata packet to a receiver are selected. The plurality of resource blocksare dynamically allocated in at least one or a combination of a time,code or frequency domain, preferably the time/frequency or time/codedomain.

Upon selecting the candidates, a data packet is transmitted (step 120)using at least one allocated RB from selected RB candidates in step 110.

Finally, the transmitter receives feedback information from the receiveron the transmitted data packets, such as acknowledgements ornon-acknowledgements messages or a quality of channel information. Basedon the feedback message, the transmitter may adapt or alter theselection strategy carried out in step 110 on the resource blockcandidates for the next transmission. In an ARQ system, the nexttransmission may be a retransmission step of at least a part of thepreviously transmitted data packet.

It should be clear to those skilled in the art that there is nonecessity to change the selected candidates for each transmission andthat a selection can be done on a “as needed” basis.

Further it will be appreciated from the below description that theselection can be alternatively based on previous transmissions orpreconfigured schemes.

In addition, it is understood that there is no requirement for thereceiver to send feedback on a regular basis, i.e., for each subsequenttransmission.

FIG. 9 illustrates the operational steps of the decoding method at thereceiver according to a preferred embodiment.

In step 150, information on the resource block candidates for potentialreception of a data packet is obtained. The candidates may either bepre-configured by the network for an individual user or receiver ordetermined based on, e.g., measurements or other link parameters of thecommunication link.

In step 160, the receiver decodes all resource block candidatespreferably parallel or in a series preferably according to a priorityscheme to detect data packets destined for the receiver.

In step 170, the receiver transmits feedback to the transmitter tooptimize the next transmission. The feedback may be interpreted by thetransmitter as an instruction or recommendation for the selectionstrategy of resource block candidates.

FIG. 10 shows a preferred embodiment for the transmitter embodied as abase station and a receiver embodied as a mobile station of a wirelesscommunication system.

The base station 200 comprises a resource allocation unit 210 for thedynamic allocation of resource blocks. In order to select the resourceblock candidates, it comprises a selection unit 230. In addition, aconventional modulator and encoder 220 provides mapping of the datapackets on the allocated resource blocks for transmission over awireless link to the receiver. For receiving feedback from the receiveras described above, a feedback evaluation unit 240 is also comprised inthe base station. All above mentioned functional units areinterconnected with each other by a conventional data bus and undercontrol of a central control unit, which has been omitted in the figurefor simplification purposes.

At the mobile station 300, corresponding functional components comprisea demodulator and decoder 320, and a resource block candidatesinformation unit 310. The information unit receives information on theselected resource block candidates either from the base station ornetwork. Alternatively, it determines the information by itself.Further, a measurement and control unit 330 is able to perform therequired communication link measurements and to detect a destined datapacket. Finally, a feedback signal generating unit 340 provides afeedback signal, such as acknowledgement, non-acknowledgement or channelquality information to the base station. The feedback signal may alsoinclude information on the resource block candidate selection.

For the location in the time-frequency grid (RBs on different PHYframes) of ARQ retransmissions, a number of RB candidates are defined.Since the user (receiver) generally knows if a retransmission takesplace (due to ACK/NACK transmission), the user tries to decode thepotentially transmitted DCIs on the RB candidates and finds the RB onwhich the retransmission has actually been scheduled. This can be seenas a kind of semi-blind detection of retransmissions, i.e., a semi-blinddetection of the DCIs associated with the retransmissions. Generally,the number of RB candidates should by significantly smaller than alltheoretically possible RBs in case of asynchronous ARQ. An example isshown in FIG. 11.

As mentioned before, according to the preferred embodiment, it isassumed that the DCI is transmitted on the same resource (RB) as thedata. Therefore, if a user identifies a DCI intended for it on one ofthe RB retransmission candidates, it can detect the retransmission dataand try to decode the data. This implies that on the RB candidates, thereceiver can distinguish a DCI intended for itself (correct DCI) fromDCIs intended for other users, since RB candidates on which its ownretransmission is not scheduled may be used for data to other users. Theidentification of the correct DCI may work, e.g., as follows:

The DCI carries a signature or an identity based on which the receivercan detect if the DCI is intended for it. This signature or identity maybe transmitted explicitly (transmitted data bits) or may be transmittedimplicitly (the data part of the DCI is scrambled/masked/colored with auser signature or identity, as in, e.g., 3GPP HSDPA).

Alternatively, the DCI does not carry a specific signature or identity,but the receiver can detect if the DCI is intended for it based on atleast one of the modulation, coding scheme or coding rate ascommunication link properties.

Furthermore, the detection can be carried out on the basis of the datacontent of the DCI, e.g., transport-block size, HARQ or MIMO parameters.

It is noted that retransmissions may be mapped onto multiple RBs, i.e.,each RB candidate essentially represents multiple RBs. Then, either theDCI may be mapped on the RB candidate or it may be mapped starting fromthe RB candidate in a known format.

The RB candidates for retransmissions may be defined according to thefollowing policies, where the policies focus on the case that all RBcandidates are in the same PHY frame (see also section FIGS. 12-14).However, without loss of generality the policies may be applied to themore general case, where the RB candidates may be on different PHYframes.

RB candidates are defined based on feedback from the user (receiver). Inone case, the feedback may be transmitted in a regular manner, e.g.,with a defined duty cycle. In another case, the feedback may betriggered by the transmitter (base station), where the trigger eithermay be an explicit feedback request by the transmitter or may be causedby actual data transmissions (e.g., transmission of a packet). Thisfeedback may be transmitted jointly explicitly or implicitly togetherwith a CQI (Channel Quality Indicator) feedback. Note that the actualdefinition of the RB candidates may either directly be indicated by theuser, which is then mandatory for the base station, or the user feedbackmay be interpreted as a recommendation, on which the RB candidatedecision of the base station is based upon. In this case, the basestation would need to inform and signal the RB candidates to the user.The following examples are given:

The user may feedback the CQI for selected (best) RBs only. Then the RBcandidates are based on these selected RBs. An example is shown in FIG.12.

Alternatively, the user may feedback a joint CQI for multiple RBs only.Then the RB candidates are based on this selected RBs.

As a variant, at a given time instant, the user may feedback acompressed CQI of RBs, e.g., by transformation in time domain by a DCT(Discrete Cosine Transform). Then the RB candidates may be defined basedon the best RBs (after reconstructing the CQIs of RBs at the basestation).

Furthermore, as an alternative to the above description with respect toFIG. 8, RB candidates may be furthermore defined depending on the RB(s)on which the previous (re)transmission or the initial transmission hasbeen scheduled. Generally, a packet transmission may be mapped onto asingle or onto multiple RBs. This may be either in a localized way or ina distributed way. Generally, this would need to be preconfigured by thenetwork and informed to the mobile station. The following lists somenon-exhaustive examples:

a) The initial transmission or previous (re)transmission has beentransmitted on RB k, then the retransmissions are transmitted within RBsk±n, i.e., in the vicinity (local band, i.e., localized) of the initialtransmission or previous (re)transmission. An example is shown in FIG.13.

b) The initial transmission or previous (re)transmission has beentransmitted on RBs k to k+l, then the retransmissions are transmittedbetween RBs k−m and l+m, i.e., in the vicinity (local band) of theinitial transmission or previous (re)transmission.

c) The initial transmission or previous (re)transmission has beentransmitted on RB k, then the retransmissions are transmitted on RBsk±m·n, with m>1 and n=1, 2, . . . , N, i.e., distributed within a givenband relative to the initial transmission or previous (re)transmission.An example is shown in FIG. 14.

d) The initial transmission or previous (re)transmission has beentransmitted on RBs k to k+l, then the retransmissions are transmitted onRBs k±m·n, with m>1 and n=1, 2, . . . , N, i.e., distributed within agiven band relative to the initial transmission or previous(re)transmission.

e) The whole system bandwidth may be segmented into M frequency-blocks,each of which contains N_(m)≧1 RBs. If the initial transmission orprevious (re)transmission is transmitted on frequency-block m the RBcandidates for the retransmission may be only on the frequency-block m.Alternatively, the retransmission RB candidates may be on anotherfrequency-block p≠m, which is preconfigured. Further, either all RBs ofa selected frequency-block may be candidates or only selected onesaccording to the examples given above.

In case the system bandwidth is wider than the bandwidth capability ofsome mobile stations, segmentation into frequency-blocks is useful. Inthis case, some mobile stations can only receive selectedfrequency-blocks. E.g., the system bandwidth is 20 MHz and is dividedinto 4×5 MHz frequency-blocks, then a mobile station with a bandwidthcapability of 5 MHz can only receive one out of 4 frequency-blocks,whereas a mobile station with a bandwidth capability of 10 MHz canreceive two adjacent out of 4 frequency-blocks. Naturally, a mobilestation with a bandwidth capability of 20 MHz can receive allfrequency-blocks.

Furthermore, as an alternative to the above description with respect toFIG. 8, it should be noted that RB candidates may be predefinedindependent of the RB on which the initial transmission or previous(re)transmission has been transmitted. Generally, this would need to bepreconfigured by the network and informed to the mobile station, e.g.,

a) RB candidates are preconfigured in a distributed manner, preferablywithin the band a mobile station can receive.

b) RB candidates are preconfigured in a localized manner, preferablywithin the band a mobile station can receive.

c) RB candidates are within a preconfigured frequency-block.

Besides the general RB candidate configuration as illustrated above, thepreferred embodiment is the case when all RB candidates for a givenretransmission are in the same PHY frame. Examples are shown in FIG. 12and FIG. 14.

Compared to the general solution, this has the benefit of potentialefficient DRX (Discontinuous Reception) operation. Moreover, this can beimplemented like synchronous ARQ, where the retransmissions have atiming relation to earlier transmissions, i.e., the timing of the RBcandidates is known to the mobile station and the RB candidates aredefined in frequency domain. Note that in this case the scheduling gainfor retransmissions is restricted to FDS, which is usually sufficient.

In the following, variants of the above-described illustrativeembodiments are described, which are apparent to those skilled in theart.

As a final variant, the DCI in retransmissions may be power adapted withrespect to the initial transmission. Depending on other configurationparameters, more or less power would be beneficial. Further, the DCIsize may be different for retransmissions than for initialtransmissions.

Depending on the RB candidate policies defined, the RB candidates fordifferent users may have the following additional properties:

a) The RB candidates overlap as little as possible. In this case the RBcandidates are defined such that RB candidates of different users arenon-identical. This allows to avoid collisions of retransmissions andshortcomings in resources for retransmissions. In case the total numberof available RBs is less than the total number of RB candidates, some RBcandidates of different users may overlap. This can be avoided, e.g., byreconfiguring the RB candidates such that the total number of RBcandidates is less than the total number of RBs. Alliteratively, the RBcandidates could be defined such that a minimum overlap exists, wherethe amount overlapping is similar for all users.

b) The RB candidates for different users overlap as much as possible.This could be seen as a virtual retransmission channel on which a kindof statistical multiplexing of retransmissions takes place. E.g., thereare N users in a system and M RB candidates are defined for each user,then these M RB candidates may be identical for all users. Note thatthis may not be possible in all cases, since some users may be allocatedon different frequency blocks.

c) The RB candidates for different users overlap partially, e.g., thereare N users in a system and M RB candidates are defined for each user.If M≦N, then these M users may have identical RB candidates, i.e., Musers share a kind of virtual retransmission channel.

As a further variation, the concept may also work for the case where theDCI is not mapped on the RB on which the data is scheduled. In thiscase, the DCI should either indicate implicitly or explicitly thelocation of the corresponding data part.

The method of the invention may be implemented not only forretransmissions but already for initial transmissions, i.e., the mobilestation would semi-blindly detect already the DCI of the initialtransmission and no SCI would be needed at all.

Typically, the semi-blind detection of DCIs on the RB candidates iscarried out in a parallel or a serial way. In case of serial semi-blinddetection, the mobile station may use smart schemes to order the RBcandidates according to priorities, e.g., the mobile station starts withthe RB candidate, which has the best actual or reported channel qualityor the mobile station starts with the RB candidate, which is closest tothe RB of the initial transmission or previous (re)transmission.

Analogue to the preferred embodiment illustrated in FIGS. 12-14, the RBcandidates may be on the same RBs in frequency domain, and then aredefined in time domain. This allows TDS of retransmissions, but not FDS.Compared to the preferred embodiment, this has the drawbacks of beingnot synchronous in time and of introducing additional delay.

In a Type I HARQ scheme the method works fine without having the DCI forretransmission, but performing semi-blind detection of theretransmission data. Theoretically, this may also work with Type II/IIIHARQ schemes, but would lead to large receiver HARQ buffer requirements,since the receiver would need to store the data of all received RBcandidates of all failed retransmissions. Further, in a worst case thereceiver would need to combine and try decoding all combinations of RBcandidates across retransmissions.

The invention claimed is:
 1. A method comprising the steps of:receiving, by a receiver, at least part of data packets and dedicatedcontrol information (DCI) destined for the receiver from a base stationon a subset of selected resource unit candidates among a plurality ofresource units defined on a shared data channel (SDCH), which areselected by the base station, a resource unit being a minimum unit fordata allocation in a combination of time and frequency domains on theSDCH, the DCI including modulation and coding information of the datapackets, wherein the DCI is mapped to a first slot of a resource unitcandidate included in said subset of selected resource unit candidatesand the at least part of the data packets is mapped to a second slot ofthe resource unit candidate which follows the first slot of the resourceunit candidate, the first slot and the second slot being provided in asingle resource unit candidate that is defined on the SDCH, and the SDCHbeing a data region which follows a control region in a time domain,wherein the control region is a shared control information region sharedby all users, comprising resource unit allocation information;attempting, by the receiver, to decode the selected resource unitcandidates to successfully decode the DCI destined for the receiver andtransmitted on said subset of selected resource unit candidates todetect the at least part of the data packets; receiving, by thereceiver, information related to the selected resource unit candidatesfrom the base station before receiving the at least part of the datapackets and the DCI; and signalling, by the receiver, a feedback messagecontaining feedback information for use by the base station to selectthe resource unit candidates in next transmission, wherein the feedbackinformation comprises a channel quality indicator (CQI) of the resourceunit candidates.
 2. The method according to claim 1, wherein the step ofattempting, by the receiver, to decode the selected resource unitcandidates is carried out in a parallel manner.
 3. The method accordingto claim 1, wherein the step of attempting, by the receiver, to decodethe selected resource unit candidates is carried out in a serial mannerwith a priority scheme.
 4. The method according to claim 1, wherein theDCI carries an identifier of the receiver for use by the receiver indecoding the DCI destined for the receiver.
 5. The method according toclaim 1, wherein the DCI is modulated and encoded using at least one ofa modulation parameter, coding parameter or transport parameter, whichallows the receiver to distinguish the DCI destined therefor from thosedestined to other receivers.
 6. A receiver apparatus comprising: areceiver configured: to receive at least part of data packets anddedicated control information (DCI) destined for the receiver apparatusfrom a base station on a subset of selected resource unit candidatesamong a plurality of resource units defined on a shared data channel(SDCH), which are selected by the base station, a resource unit being aminimum unit for data allocation in a combination of time and frequencydomains on the SDCH, the DCI including modulation and coding informationof the data packets, wherein the DCI is mapped to a first slot of aresource unit candidate included in said subset of selected resourceunit candidates and the at least part of the data packets is mapped to asecond slot of the resource unit candidate which follows the first slotof the resource unit candidate, the first slot and the second slot beingprovided in a single resource unit candidate that is defined on theSDCH, and the SDCH being a data region which follows a control region ina time domain, wherein the control region is a shared controlinformation region shared by all users, comprising resource unitallocation information; and to receive information related to theselected resource unit candidates from the base station before receivingthe at least part of the data packets and the DCI; and one or moreprocessors configured: to attempt to decode the selected resource unitcandidates to successfully decode the DCI destined for the receiverapparatus and transmitted on said subset of selected resource unitcandidates to detect the at least part of the data packets; and tosignal a feedback message containing feedback information for use by thebase station to select the resource unit candidates in nexttransmission, wherein the feedback information comprises a channelquality indicator (CQI) of the resource unit candidates.
 7. The receiverapparatus according to claim 6, wherein the one or more processors areconfigured to attempt to decode the selected resource unit candidates ina parallel manner.
 8. The receiver apparatus according to claim 6,wherein the one or more processors are configured to attempt to decodethe selected resource unit candidates in a serial manner with a priorityscheme.
 9. The receiver apparatus according to claim 6, wherein the DCIcarries an identifier of the receiver apparatus for use by the receiverapparatus in decoding the DCI destined for the receiver apparatus. 10.The receiver apparatus according to claim 6, wherein the DCI ismodulated and encoded using at least one of a modulation parameter,coding parameter or transport parameter, which allows the receiverapparatus to distinguish the DCI destined therefor from those destinedto other receiver apparatuses.